Very young children who are late in reaching early language milestones (production of first words, growth of vocabulary and combining words) may be at risk for later language impairment and/or learning disability. Because standardized tests and clinically reliable measures for determining which children will develop normally and which will remain delayed are not yet available, they are also at risk for being missed by pediatricians and other professionals on whom parents rely to make appropriate early referrals. The major purpose of this project is to identify factors in children 18- to 24-months old which predict potential later language and learning deficits. This, in turn, will allow appropriate early identification and referral. The studies proposed are designed to identify the nature of the relationship(s) between language and other aspects of nonverbal cognition in late talking toddlers, and to follow their development in those domains over a period of 4 years. Late talking toddlers will be compared to normal children of the same age, normal children at the same level of language development, mentally retarded children, and linguistically precocious children, at each test time. The 4 control groups will be followed longitudinally as well. In the last year, the experimental subjects will be compared to a group of children (matched for age) who have been diagnosed as language impaired and who are enrolled in therapy. For all groups, development in linguistic and nonlinguistic domains will be measured and examined for associations and dissociations within and across domains. Specific domains to be studied are language comprehension and production, use of symbolic gestures, spatial cognition and concept formation and categorization. These domains will be analyzed to provide profiles of language and other cognitive variables which will serve as markers for those who are or are not likely to catch up linguistically. Since data will also be gathered longitudinally, information about the course of development will be obtained, giving information about the processes involved in catching up or falling behind. Longitudinal data will provide information which will be useful beyond the immediate goal of identifying predictors of risk for language and/or learning impairment. Specifically, the information will be used for the design of research on early assessment and intervention.